Simplistic NJFET RIAA - Page 912 - diyAudio
Go Back   Home > Forums > Source & Line > Analogue Source

Analogue Source Turntables, Tonearms, Cartridges, Phono Stages, Tuners, Tape Recorders, etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 20th January 2013, 08:06 PM   #9111
RCruz is offline RCruz  Switzerland
diyAudio Member
 
RCruz's Avatar
 
Join Date: Sep 2006
Location: Wallis
Blog Entries: 1
Salas

Sorry fo the out of scope question but just for learning purposes,.... in my most recent build, If I used only one common Rs for both k170 in the input, what value should I choose ?

I am using one 3.9 per leg... should I need to use only one 2 x3.9r = 7.8r ?
__________________
RC
  Reply With Quote
Old 20th January 2013, 08:11 PM   #9112
Salas is online now Salas  Greece
diyAudio Chief Moderator
 
Salas's Avatar
 
Join Date: Oct 2002
Location: Athens-Greece
No, to the contrary, halve the original discrete value.
  Reply With Quote
Old 20th January 2013, 08:18 PM   #9113
RCruz is offline RCruz  Switzerland
diyAudio Member
 
RCruz's Avatar
 
Join Date: Sep 2006
Location: Wallis
Blog Entries: 1
I see I have a long way before me.....

Would you please give me a hint on how to calc Rs and Rd for a circuit using two fets ?
__________________
RC
  Reply With Quote
Old 20th January 2013, 08:41 PM   #9114
Salas is online now Salas  Greece
diyAudio Chief Moderator
 
Salas's Avatar
 
Join Date: Oct 2002
Location: Athens-Greece
If they are exactly matched then no one will current hog if with a common Rs. Since you double the current flow you need half the value to maintain the same local feedback (degeneration). Other than when using expensive boutique resistors and need economize there is no advantage VS one Rs per JFet which leaves slack for not that matched semis also. Rd? You mean the Jfets current sourcing resistor? That one derives from the total current drawn by the Jfets plus what you need flow through the common base cascoding BJT to have a range for TP1/TP2 centering. In conjunction with B+. That is why we use a trimmer locally to vary B+ for that CCS resistor. Its a balancing act. You solve against bias currents and B+.
  Reply With Quote
Old 20th January 2013, 09:05 PM   #9115
RCruz is offline RCruz  Switzerland
diyAudio Member
 
RCruz's Avatar
 
Join Date: Sep 2006
Location: Wallis
Blog Entries: 1
Now I see...


To keep the same Vgs at double current we need half the Rs.


As for the rest... digest will be done tomorow
__________________
RC
  Reply With Quote
Old 20th January 2013, 09:08 PM   #9116
Salas is online now Salas  Greece
diyAudio Chief Moderator
 
Salas's Avatar
 
Join Date: Oct 2002
Location: Athens-Greece
...Buzz is quiet...Maybe he managed to listen without problems? Hmm, we will know sooner or later.
  Reply With Quote
Old 20th January 2013, 11:50 PM   #9117
diyAudio Member
 
buzzforb's Avatar
 
Join Date: Oct 2010
Location: Burlington, NC
Couldnt get it finished in time. Too many other activities took away the afternoon. Will resume tomorrow. It will give me the chance to get the other sslv up and running. Thanks for the help. I now understand the current hogging issue. Stepping away and thinking did me some good. Already got new boards drawn and correct jfets coming, as i do not have enough low idss fets to do one right. It willbe SMD again, with this one using Susumu. Should be good comparison of smd choices. I am going to bed. Long day. Thanks again.
__________________
...Shape the sound , Man!
  Reply With Quote
Old 21st January 2013, 09:19 AM   #9118
RCruz is offline RCruz  Switzerland
diyAudio Member
 
RCruz's Avatar
 
Join Date: Sep 2006
Location: Wallis
Blog Entries: 1
So, using 3,9 for Rs, you use the jfets almost at Idss.
In my case Vgs = 29mV so I have 0.0074 Id on each fet
Double current (0.0149) flows on R13 (1k5) droping 22V
For R4 (2k2) we need 4Vdrop so current is 0.0018 that drops 3V on R13(1k5)
Total drop on R13 is 22+3=25v, so we need Vdd over R13 to be 33v so we have 8v on the bjt emitter.

35Vin-33=2V that must be droped on the trimmer... (0.0149+.0018)=0.0167 over the trimmer so it must be around 120r.

Easy to do on paper.. letīs see if I can compute it.....
__________________
RC
  Reply With Quote
Old 21st January 2013, 09:26 AM   #9119
RCruz is offline RCruz  Switzerland
diyAudio Member
 
RCruz's Avatar
 
Join Date: Sep 2006
Location: Wallis
Blog Entries: 1
As I use LTSpice for sim, and do not have mA k170 (only 11mA) and no BC560c, my sim is no good for this purpose.
__________________
RC
  Reply With Quote
Old 21st January 2013, 02:33 PM   #9120
RCruz is offline RCruz  Switzerland
diyAudio Member
 
RCruz's Avatar
 
Join Date: Sep 2006
Location: Wallis
Blog Entries: 1
Quote:
Originally Posted by RCruz View Post
As I use LTSpice for sim, and do not have mA k170 (only 11mA) and no BC560c, my sim is no good for this purpose.
Almost done.

Salas, would you please post 1st stage gain in the case using double k170 in the input ?
__________________
RC
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



New To Site? Need Help?

All times are GMT. The time now is 05:32 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright Đ1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2